use or refused to participate in either the NHSDA or the DC*MADS studies. Thus, these estimates of one-third and two-thirds have some unknown degree of associated error.³

NIDA's Monitoring the Future survey provides the most accurate data available on drug use among secondary school students, but it has the same limitations as the NHSDA in its ability to estimate the hard-core subpopulation of drug users that includes injection drug users. However, like the NHSDA, the Monitoring the Future survey does pick up a small but substantial number of its sampled population who acknowledge having injected drugs. In 1992, 1.7 percent of high school seniors reported having injected a drug during their lives, and 0.8 percent did so in the past year. In 1993, 1.4 percent reported having injected during their lives, and 0.7 percent did so in the past year (O'Malley, unpublished data).

The Centers for Disease Control and Prevention conducted several nationally representative surveys of students in grades 9-12 asking about various risk behaviors, including injection of drugs (Centers for Disease Control and Prevention, 1992). The 1990 Youth Risk Behavior Survey showed 1.5 percent lifetime prevalence for grade 10, and 1.3 percent for grade 12, which are fairly close to the corresponding figures from the Monitoring the Future surveys (1.4 percent and 1.7 percent, respectively). Another noteworthy finding is that studies in both San Francisco and New York report that sharing appears to be more frequent among younger injectors (Guydish et al., 1990; Kleinman et al., 1990), who are typically not very well represented in current needle exchange programs in this country (see the section on the demographics of program participants in Chapter 3).

In sum, across a number of surveys of the type that would be expected to underestimate injection drug use, there is a fair amount of consistency, suggesting a prevalence rate that is clearly not zero and may be as high as 1 to 2 percent among young Americans. None of the surveys show any dramatic shifts in recent years.

Another perspective that is important to consider in light of broader population-based surveys of injection drug users is the limited number of injection drug users that are in treatment. It is estimated that between 10 and 20 percent of injection drug users are in drug treatment at any give time (Centers for Disease Control and Prevention, 1990; Office of Technology Assessment, 1990; Wiley and Samuel, 1989; Schuster, 1988).